Door Holders and Closers  

These are either electromagnet Holders that are wired into the fire alarm system and hold the fire door open, then releasing when the fire alarm system sounds or

Door Closers which are the arm type and pull the fire door shut when the fire alarm sounds.

Also available are the battery operated Dorgard units which attach to the bottom of the door and then release when they "hear" the fire alarm bells or sounds being activated. Download the Dorgard brochure here.